1. Field of Invention
The invention relates to electro-optical systems such as backlight modules of liquid crystal displays, cell phone displays, and personal digital assistants, and particularly to the light-guide module for emitting particular polarized light beam by converting light-beam polarization.
2. Related Art
Many electro-optical systems, such as backlight modules of liquid crystal displays, cell phone displays, and personal digital assistants, are non-lighting displaying apparatus, so adding light sources for displaying is needed.
The increased brightness demand of electro-optical systems on the market makes good use of light sources' electro-optical systems more and more important. Most liquid crystal displays have polarized plates installed close to outlets of light sources to let particular polarized light beams pass through and to let other light beams be reflected for emitting particular polarized light beams. However, the brightness of liquid crystal displays is limited by the amount of other light beams which exceed fifty percentages.
Two main body types of backlight modules are a single-surface electroluminesence (EL) and a cold cathode fluorescent lamp (CCFL).
As shown in FIG. 1, one main body type of liquid crystal display backlight modules is a single-surface EL 1. A single-surface EL 1 consists of a reflecting film 11, an insulating layer 12, a luminant layer 13, and a transparent electrode 14. Non-polarized light beams from the top surface of the luminant layer 13 pass through the transparent electrode 14. Non-polarized light beams from the bottom surface of the ruminant layer 13 pass through the insulating layer 12 and are reflected by the reflecting film 11, then pass through the insulating layer 12, the luminant layer 13, and the transparent electrode 14 in that order. Light beams separated by polarization of the polarized plate 15 result in over fifty-percent light energy loss of non-polarized light beams from the single-surface EL 1. Otherwise, non-polarized light beams from the bottom surface of the luminant layer 13 are absorbed by the reflecting film 11 when reflecting. So the single-surface EL 1 causes a high power consumption and limited displaying quality.
As shown in FIG. 2, one main body type of liquid crystal display backlight modules is a CCFL 2. A CCFL 2 consists of a guiding plate 21, a diffuse plate 22, a prism plate 23, a reflecting plate 24, and a light source 25. Non-polarized light beams from the light source 25 pass through the top and bottom surfaces of the guiding plate 21. Non-polarized light beams passing through the top surface of the guiding plate 21 pass the diffuse plate 22 and the prism plate 23, then emit out of the CCFL 2. Non-polarized light beams passing through the bottom surface of the guiding plate 21 are reflected by the reflecting plate 24 and pass the guiding plate 21, the diffuse plate 22, and the prism plate 23 in that order, then emit out of the CCFL 2. Also, light beams separated by polarization of the polarized plate 15 result in over fifty-percent light energy loss of non-polarized light beams.
The main reason of small size, low brightness, and a high power consumption of the liquid crystal display is light energy loss in the polarized plate 15, even taking a single-surface EL or a CCFL as the main body of backlight modules of liquid crystal displays. Instead of the polarized plate, a splitter for separating non-polarized light beams is used to solve light energy loss problems, and a transformer for converting polarization of light beams is used to increase the ratio of light passing the polarized plate. The splitter and the transformer are each disclosed in U.S. Pat. No. 6,005,713 and U.S. publication number 2001/0033417, respectively. For using in the range of the visible light spectrum, the splitter has to be a multi-layer film with at least 400 layers. The splitter is formed by alternately stacking two different materials with uniform force, so the refractive index and thickness has to be accurately controlled.
The transformer is a coating or a rough surface, but it is hard to achieve the goal of high transforming efficiency without an optimal design. On the contrary, light energy losses via absorbing and scattering by the transformer increase.
From above descriptions, it is important to design a light-guide module for emitting particular polarized light beams to achieve the goals hereinafter. The first goal is making a liquid crystal display with a larger size, higher brightness, and low power consumption by light-guide modules with high efficiency splitters and transformers. The second goal is making a simplified structure of light-guide modules.